Damage detection method of wire rope, and signal processor and damage detection device used for damage detection of wire rope

ABSTRACT

A magnetic detector includes permanent magnets that magnetize a wire rope W in the longitudinal direction, and a search coil that detects a change in the cross sectional area of the wire rope W magnetized by the permanent magnets. The magnetic detector is provided so as to surround a part of the wire rope W. Prior to inspection, the magnetic detector is moved back and forth at least three times across an inspection range of the wire rope W. After the magnetic detector is moved back and forth, the change in the cross sectional area, that is, damage to the wire rope W is inspected by using signals outputted from the search coil.

CROSS REFERENCE TO RELATED APPLICATIONS

This Continuation Application claims the benefit of U.S. Continuationapplication Ser. No. 16/439,756 filed on Jun. 13, 2019, and titled“Damage Detection Method Of Wire Rope, And Signal Processor And DamageDetection Device Used For Damage Detection Of Wire Rope” which claimsthe benefit of and priority to PCT International Application No.PCT/JP2016/087019 filed on Dec. 13, 2016, the entire disclosures of theapplications being considered part of the disclosure of this applicationand hereby incorporated by reference.

TECHNICAL FIELD

The present invention relates to a damage detection method of a wirerope, and a signal processor and a damage detection device used fordamage detection of a wire rope.

BACKGROUND ART

Japanese Patent Application (Laid-Open No. 2002-5896) discloses aninspection device that inspects a wire rope by using the magnetic fluxleakage method.

In the magnetic flux leakage method, a wire rope is magnetized in thelongitudinal direction by using magnets of the inspection device, andmagnetic flux leaked from a damaged part of the wire rope is detected.An elongated magnetic body such as a wire rope may be magnetized due toan influence of earth magnetism during or after manufacture, andmagnetic poles may be originally formed in both end portions of the wirerope. Therefore, when magnetic force of the magnets provided in theinspection device is weak, the magnetizing directions (magnetic axes) ofthe wire rope in an inspection range are not uniform due to an influenceof the magnetic poles of both the end portions of the wire rope. As aresult, output signals of the inspection device, in particular, outputsignals of both end parts of the inspection range may be unstable (S/Nratio may be deteriorated). By using magnets having strong magneticforce, it is possible to make the magnetizing directions of theinspection range uniform to some extent. However, since magnets havingstrong magnetic force are heavy, the inspection device is less easilyconveyed.

DISCLOSURE OF THE INVENTION

An object of the present invention is to make the magnetizing directionsof an inspection range of a wire rope uniform.

A further object of the present invention is to improve the S/N ratio ofsignals outputted from a damage detection device of a wire rope.

Further, an object of the present invention is to equally magnetize awire rope over the entire circumference, and to prevent damage to thewire rope at the time of inspection

A damage detection method of a wire rope according to the presentinvention is a damage detection method of a wire rope using a portabledamage detection device which is provided so as to surround a part ofthe wire rope in the longitudinal direction over the entirecircumference, the portable damage detection device including amagnetizing device (means) that magnetizes the wire rope in thelongitudinal direction, and a search coil that detects a change in thecross sectional area of the wire rope in an inspection range magnetizedby the magnetizing device, the damage detection method beingcharacterized by including moving the damage detection device back andforth on the wire rope the predetermined number of times across theinspection range of predetermined length of the wire rope, and after thedamage detection device is moved back and forth the predetermined numberof times, recording signals outputted from the search coil.

According to the present invention, prior to inspection of the wire ropeusing the damage detection device, the damage detection device is movedback and forth the predetermined number of times across the inspectionrange of the predetermined length of the wire rope. Thereby, it ispossible to align the magnetizing directions (magnetic axes) in theinspection range of the wire rope. By moving the damage detection deviceback and forth in the inspection range, there is no large divergencebetween output signals from the search coil in an outbound move andoutput signals from the search coil in a return move. It is possible toalign the magnetizing directions (magnetic axes) in the inspectionrange, and improvement of inspection precision is realized.

Preferably, the damage detection device is moved until the damagedetection device exceeds both ends of the inspection range of thepredetermined length of the wire rope. It is possible to align themagnetizing directions of the entire inspection range.

In an aspect, the damage detection device is moved back and forth atleast three times. It is possible to obtain stable output signals.

It is possible to set (adjust) length of the inspection rangearbitrarily. In a case where the wire rope is longer than the inspectionrange, it is possible to inspect the wire rope over the entire lengththereof by gradually displacing the inspection range. Every time theinspection range is displaced, by moving the damage detection deviceback and forth across a new inspection range prior to inspection of thenew inspection range, it is possible to inspect the wire rope over theentire length with good precision.

The present invention also provides a signal processor suitable fordamage detection of the wire rope described above. The signal processoraccording to the present invention includes a voltage signal receivingdevice (means) that receives an input of voltage signals correspondingto the change in the cross sectional area of a wire rope, the voltagesignals outputted from a search coil of a portable damage detectiondevice which is provided so as to surround a part of the wire rope inthe longitudinal direction over the entire circumference, the portabledamage detection device including a magnetizing device (means) thatmagnetizes the wire rope in the longitudinal direction, and the searchcoil that detects a change in the cross sectional area of the wire ropein an inspection range magnetized by the magnetizing device (means), aconverting device (means) that converts the voltage signals received bythe voltage signal receiving device into magnetic flux signals, asmoothing device (means) that smooths the magnetic flux signalsconverted by the converting device and calculates smoothed magnetic fluxsignals, and a subtracting device (means) that subtracts the smoothedmagnetic flux signals from the magnetic flux signals.

The present invention also provides a method suitable for controllingthe signal processor described above. The signal processing methodaccording to the present invention includes receiving, by a voltagesignal receiving device (means), an input of voltage signalscorresponding to the change in the cross sectional area of a wire rope,the voltage signals outputted from a search coil of a portable damagedetection device which is provided so as to surround a part of a wirerope in the longitudinal direction over the entire circumference, theportable damage detection device including a magnetizing device (means)that magnetizes the wire rope in the longitudinal direction, and thesearch coil that detects a change in the cross sectional area of thewire rope in an inspection range magnetized by the magnetizing device,converting the received voltage signals into magnetic flux signals by aconverting device (means), calculating smoothed magnetic flux signals bysmoothing the converted magnetic flux signals by a smoothing device(means) and subtracting the smoothed magnetic flux signals from themagnetic flux signals by a subtracting device (means).

When the magnetic poles are originally formed in both the end portionsof the wire rope due to an influence of earth magnetism during or aftermanufacture, output signals (voltage signals or magnetic flux signals)in particular, in both end parts of the inspection range may beinfluenced by the magnetic poles in both the end portions of the wirerope. According to the present invention, by subtracting the smoothedmagnetic flux signals by smoothing the magnetic flux signals from themagnetic flux signals, it is possible to cancel or reduce an amount ofinfluence of the magnetic poles in both the end portions of the wirerope included in the output signals in both the end parts of theinspection range. Since the S/N ratio of the output signals is improved,it is possible to more accurately detect occurrence of damage to thewire rope, and a degree and an occurrence place of the damage.

For example, the moving average method can be used for the smoothingdevice. The moving average method may use simple moving average orweighted moving average. As a matter of course, both the simple movingaverage and the weighted moving average can be used.

The present invention also provides a portable damage detection deviceincluding a moving mechanism suitable for damage detection of the wirerope described above. The portable damage detection device including themoving mechanism according to the present invention includes a portabledamage detection device including a magnetizing device (means) which hasa columnar internal space through which a wire rope passes, the internalspace having a diameter larger than a diameter of the wire rope, themagnetizing device that magnetizes the wire rope in the longitudinaldirection, the magnetizing device being arranged in an annular shape,and a search coil that detects a change in the cross sectional area ofthe wire rope in an inspection range magnetized by the magnetizingdevice, the search coil being arranged in an annular shape, and a movingmechanism including rotatable support rollers respectively attached toboth end portions of the portable damage detection device at equal angleintervals, the support rollers that support the wire rope from fourdirections around the wire rope at both the end portions, and therespective support rollers in both the end portions of the portabledamage detection device are attached in such a manner that the crosssectional center of the wire rope matches with the cross sectionalcenter of the internal space.

Since the wire rope passes through the center of the internal space ofthe portable damage detection device, a distance between the wire ropeand the magnetizing device arranged in an annular shape becomes equalover the entire circumference, and it is possible to equally magnetizethe wire rope over the entire circumference. Further, since the wirerope is not brought into contact with an inner peripheral surface of theinternal space of the damage detection device, damage due to contactbetween the wire rope and the damage detection device does not occur. Itis possible to smoothly move the portable damage detection device alongthe longitudinal direction of the wire rope

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a front view of a portable wire rope damage detection device;

FIG. 2 is a side view of the portable wire rope damage detection devicealong the line II-II of FIG. 1 ;

FIG. 3 is a sectional view schematically showing an internal structureof a magnetic detector;

FIG. 4 shows arrangement of permanent magnets;

FIG. 5 shows a state where the magnetic detector is being moved in aninspection range of a wire rope;

FIG. 6 is a graph showing output signals when the magnetic detector ismoved back and forth;

FIG. 7 is a flowchart showing a flow of processing of a signalprocessor;

FIG. 8 shows voltage waveforms outputted from a search coil;

FIG. 9 shows waveforms of magnetic flux amounts;

FIG. 10 shows waveforms of magnetic flux amounts after simple movingaverage

FIG. 11 shows waveforms of magnetic flux amounts after polynomial fitweighted moving average; and

FIG. 12 shows waveforms of magnetic flux amounts after correction.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 is a front view of a portable wire rope damage detection device.FIG. 2 is a side view of the portable wire rope damage detection devicealong the line II-II of FIG. 1 .

A portable wire rope damage detection device 1 includes a magneticdetector 10, and a moving mechanism 20 for moving the magnetic detector10 along a wire rope W.

The magnetic detector 10 is formed in a cylindrical shape, and includesa columnar internal space 10A through which the wire rope W passes, theinternal space having a diameter larger than a diameter of the wire ropeW. The magnetic detector 10 includes a pair of openable/closablehalf-cylindrical bodies 10L, 10R coupled at two hinges 17 which areprovided and spaced from each other in the front and back direction(cylindrical axis direction), and the half-cylindrical bodies 10L, 10Rcan be opened to both sides on the hinges 17. By enclosing (embracing)the wire rope W from both the sides by the two half-cylindrical bodies10L, 10R, the magnetic detector 10 is attached to the wire rope W.Hereinafter, for convenience of description, one end of the magneticdetector 10 in the front and back direction (cylindrical axis direction)(left end in FIG. 1 ) will be called as one end portion, and the otherend (right end in FIG. 1 ) will be called as the other end portion.

The moving mechanism 20 includes a pair of moving mechanisms 20L, 20Rrespectively attached to the half-cylindrical bodies 10L, 10R (see FIG.2 ).

The moving mechanisms 20L, 20R are made symmetrically in the front andback direction (see FIG. 1 ), and also made symmetrically in the leftand right direction (see FIG. 2 ). On an outer surface of each of thehalf-cylindrical bodies 10L, 10R, four semi-circular fins 15 projectingoutward are fixed and spaced from each other in the front and backdirection and in the circumferential direction. A screw hole is formedin each of the fins 15, and a bar 23 extending in the front and backdirection is attached to one pair of fins 15 aligned in the front andback direction. With reference to FIG. 2 , when the portable wire ropedamage detection device 1 is seen from the side, four bars 23 areattached at positions corresponding to four corners around thecylindrical magnetic detector 10.

Fan-shaped plates 21L, 21R are fixed to each of both ends of the twobars 23 aligned in the up and down direction when seen from side. Tworotatable support rollers 25L are fixed to an outer surface of thefan-shaped plate 21L via support members and spaced from each other, andtwo rotatable support rollers 25R are fixed to an outer surface of thefan-shaped plate 21R via support members and spaced from each other. Inthe one end portion, four support rollers 25L, 25R are provided at equalangle intervals when seen from the side, and in the other end portion,four support rollers 25L, 25R are also provided at equal angle intervalswhen seen from the side. An inscribed circle of four support rollers25L, 25R provided in each of the one end portion and the other endportion has the same diameter as the diameter of the wire rope W, andthe inscribed circle of the support rollers 25L, 25R is a concentriccircle to a circular cross section of the wire rope W.

The wire rope W passing through the internal space 10A of the magneticdetector 10 is supported from four directions around the wire rope. Asdescribed above, four support rollers 25L, 25R provided in each of theone end portion and the other end portion are provided in such a mannerthat the inscribed circle of the support rollers 25L, 25R has the samediameter as the diameter of the wire rope W and the inscribed circle ofthe support rollers 25L, 25R is the concentric circle to the circularcross section of the wire rope W. That is, in each of the one endportion and the other end portion of the portable wire rope damagedetection device 1, the wire rope W is supported by four support rollers25L, 25R in such a manner that the cross sectional center of the wirerope W matches with the cross sectional center of the internal space10A. Thereby, the wire rope W is positioned on the center of theinternal space 10A of the magnetic detector 10. As described later, themagnetic detector 10 includes plural permanent magnets aligned in anannular form inside thereof. Since the wire rope W passes through thecenter of the internal space 10A of the magnetic detector 10, a distancebetween the wire rope W and the permanent magnets aligned in an annularform becomes equal over the entire circumference, and it is possible toequally magnetize the wire rope W over the entire circumference.Further, since the wire rope W is not brought into contact with an innerperipheral surface of the internal space 10A of the magnetic detector10, damage due to contact between the wire rope W and the magneticdetector 10 does not occur. It is possible to smoothly move the magneticdetector 10 along the longitudinal direction of the wire rope W.

For support members of the support rollers 25L, 25R, it is possible todetachably attach support rollers 25L, 25R having different diameters.In a case where a wire rope W having a small diameter is inspected,support rollers 25L, 25R having a large diameter are attached, and in acase where a wire rope W having a large diameter is inspected, supportrollers 25L, 25R having a small diameter are attached. Even when thewire rope W has a difference diameter but a smaller diameter than adiameter of a cross section of the internal space 10A of the magneticdetector 10, it is possible to attach the magnetic detector 10, and itis possible to position the wire rope W on the center of the internalspace 10A.

With reference to FIG. 1 , a support member is fixed to the outersurface of the plate 21R provided on the other end side (right side inFIG. 1 ), and a roller 51 is attached to a leading end of the supportmember. The roller 51 is in contact with a front surface of the wirerope W. When the magnetic detector 10 is moved along the wire rope W,the roller 51 is rotated. A rotary encoder 52 is fixed to a rotationshaft of the roller 51, and a moving distance of the magnetic detector10 (position of the magnetic detector 10) is measured by this rotaryencoder 52.

FIG. 3 is a vertically sectional view schematically showing an internalstructure of the magnetic detector 10. FIG. 4 schematically shows across sectional view along the line IV-IV of FIG. 3 , and showsarrangement of the permanent magnets provided in the magnetic detector10.

In the magnetic detector 10, two rows of eighteen permanent magnets 11aligned at equal intervals in an annular form are provided on the oneend side (left side in FIG. 3 ), and two rows of eighteen permanentmagnets 12 aligned at equal intervals in an annular form are provided onthe other end side (right side in FIG. 3 ). Any of the permanent magnets11 on the one end side are arranged in such a manner that an S pole isdirected to the center of the magnetic detector 10 and an N pole isdirected outward. Any of the permanent magnets 12 on the other end sideare arranged in such a manner that an N pole is directed to the centerof the magnetic detector 10 and an S pole is directed outward. Asdescribed above, the magnetic detector 10 is formed from the pair ofhalf-cylindrical bodies 10L, 10R. Thus, nine of the eighteen permanentmagnets 11, 12 aligned in an annular form are provided in thehalf-cylindrical body 10L on one side, and the remaining nine areprovided on the half-cylindrical body 10R on the other side. The numberof the permanent magnets 11, 12 can be arbitrarily adjusted. Thepermanent magnets 11 and 12 may be connected by a yoke (not shown).

An annular search coil 13 is provided in a center part of the magneticdetector 10 in the front and back direction. One search coil 13 may beprovided, or two annular search coils 13 may be provided side by sideand spaced from each other in the front and back direction and these maybe differentially connected. The search coil 13 is formed in an annularshape by connecting connectors (not shown) respectively provided in bothends of the search coil. When the magnetic detector 10 is attached tothe wire rope W, both the ends of the connectors are disconnected.

Magnetic flux generated from the permanent magnets 11, 12 forms amagnetic loop passing through the wire rope W, and thereby, the wirerope W is magnetized. When, for example, deterioration progresses anddamage is accumulated in the wire rope W, a change (reduction) in thecross sectional area of the wire rope (reduction in the rope diameter)appears in the damaged part (such as a worn part or a corroded part).The magnetic flux passing through the magnetized wire rope W isproportional to the cross sectional area of the wire rope W. Thus, achange in the magnetic flux passing through the wire rope W appears inthe damaged part. When the magnetic detector 10 passes through thedamaged part of the magnetized (saturation-magnetized) wire rope W,electromotive force is generated in the search coil 13 by a change inmagnetic flux interlinked with the search coil 13, and this appears as apeak in output signals of the search coil 13. Based on the outputsignals of the search coil 13, it is possible to detect the change inthe cross sectional area of the wire rope W, that is, the damaged partoccurring in the wire rope W.

An elongated magnetic body such as the wire rope W may be magnetized inthe longitudinal direction upon receiving an influence of earthmagnetism during or after manufacture, and magnetic poles may beoriginally formed in both end portions of the wire rope W. Only bymoving the magnetic detector 10 (permanent magnets 11, 12) once on thewire rope W, it may be difficult to make the magnetizing directions(magnetic axes) of the wire rope W uniform.

FIG. 5 schematically shows a state where the magnetic detector 10 isbeing moved back and forth in an inspection range of predeterminedlength of the wire rope W. A signal processor 90 is connected to themagnetic detector 10 via a signal cable, and the output signals from thesearch coil 13 and output signals from the rotary encoder 52 are givento the signal processor 90 via the signal cable. As described later, inorder to make the magnetizing directions of the entire inspection rangeuniform, the magnetic detector 10 is preferably moved until the magneticdetector 10 exceeds both ends of the inspection range.

FIG. 6 is a graph showing output signals outputted from the magneticdetector 10 when the magnetic detector 10 is moved consecutively eighttimes (moved back and forth four times) across the inspection range ofthe predetermined length. FIG. 6 shows the output signals of themagnetic detector 10 when the magnetic detector 10 is moved back andforth four times across the inspection range of length of about 4meters. In the graph of FIG. 6 , the horizontal axis indicates thedistance (position of the magnetic detector 10), and the vertical axisindicates the output signals (magnetic flux (Wb)).

With reference to FIG. 6 , regarding the output signals when themagnetic detector 10 is moved back and forth across the inspectionrange, it is found that a change is large at the beginning (divergencebetween an outbound move and a return move is large) and force ofmagnetizing the wire rope W is weak. As back and force movement isrepeated, the change becomes smaller (divergence between the outboundmove and the return move becomes smaller) and the force of magnetizingalso becomes stronger. Upon the sixth move (return), the seventh move(outbound), and the eighth move (return), there is almost no change inthe output signals.

That is, by moving the magnetic detector 10 back and forth several timesacross a predetermined inspection range of the wire rope W, themagnetizing directions (magnetic axes) in the inspection range becomeuniform, and it is possible to stabilize the output signals.

The number of times the magnetic detector 10 is moved back and forthalso depends on magnetic force of the permanent magnets 11, 12 providedin the magnetic detector 10. When permanent magnets having strongmagnetic force are used, the output signals can be stabilized by theless number of times the magnetic detector is moved. However, magnetshaving strong magnetic force are generally heavy and inhibit portabilityof the magnetic detector 10. In consideration with the portability ofthe magnetic detector 10, it is proper to use such permanent magnets 11,12 that stable output signals can be obtained by moving the magneticdetector 10 back and forth three times across the inspection range.

FIG. 7 is a flowchart showing actions of the signal processor 90 thatprocesses the signals outputted from the magnetic detector 10.

First, the range of the wire rope W to be inspected is determined, andthe magnetic detector 10 is moved back and forth at least three timesacross the inspection range. As described above, the magnetizingdirections in the inspection range become uniform. Signals outputtedfrom the search coil 13 when the magnetic detector 10 is moved back andforth initially are not recorded (for example, destroyed).

After back and forth movements of the magnetic detector 10 are finished,inspection of the inspection range is started (recording of the outputsignals is started). The magnetic detector 10 is moved from one end tothe other end of the inspection range along the wire rope W. The outputsignals from the search coil 13 and the rotary encoder 52 are given tothe signal processor 90 and recorded in a memory provided in the signalprocessor 90 (Step 61).

A graph of FIG. 8 shows waveforms representing a change in the outputsignals (voltage values) of the search coil 13 when the magneticdetector 10 is moved back and forth once across a predeterminedinspection range.

As described above, when damage is present in the wire rope W, a changein the magnetic flux due to the change in the cross sectional areaoccurs, and electromotive force is generated in the search coil 13. Thegraph of FIG. 8 shows both a waveform representing a change in voltagegenerated in the search coil 13 when the magnetic detector 10 (searchcoil 13) is moved from one end to the other end of the inspection range(outbound), and a waveform representing a change in voltage generated inthe search coil 13 when the magnetic detector 10 is moved from the otherend to one end of the inspection range (return). Since polarity of thevoltage generated in the search coil 13 is reversed between the outboundmove and the return move, substantially up-down symmetric waveforms areshown on the graph.

Since the wire rope W is made by twisting a strand which is made bytwisting plural wires, spiral projections and recesses (unevenness) areformed on the front surface of the wire rope W. The change in themagnetic flux also occurs from the projections and recesses on the frontsurface of the wire rope W. Therefore, even in a part where no damageoccurs in the wire rope W, the change in the voltage is detected.

In a case where damage is present in the wire rope W, peak values(noticeable voltage values) appear among the output signals from thesearch coil 13. When a degree of the damage is higher, a change amountof the cross sectional area of the wire rope (change amount of themagnetic flux) becomes larger, and hence the peak values become larger.

It is possible to judge occurrence of damage present in the wire rope W,and a degree and a place of the damage by using the output signals(voltage values) from the search coil 13 (graph of FIG. 8 ). However,values of the output signals from the search coil 13 are changed inaccordance with moving speed of the magnetic detector 10.

Returning to FIG. 7 , in order to cancel the moving speed of themagnetic detector 10, the signal processor 90 executes processing oftime-integrating the output signals (voltage values) from the searchcoil 13 and converting into the magnetic flux (magnetic flux amounts)(step 62).

FIG. 9 shows changes in the magnetic flux amounts obtained bytime-integrating changes in the voltage values shown in FIG. 8 . Thevertical axis of the graph indicates the magnetic flux (Wb) (changes inthe magnetic flux).

It is found that both left and right ends 81, 82 of waveforms shown inFIG. 9 stand up largely. As described above, this appears in a casewhere the wire rope W is magnetized in the longitudinal direction uponreceiving the influence of earth magnetism during or after manufactureand magnetic poles are formed in both the end portions of the wire ropeW. That is, stand-up of both the left and right ends 81, 82 of thewaveforms shown in FIG. 9 does not represent the magnetic flux detecteddue to presence of the damage in the wire rope W but is so-called noisesignals appearing in a case where the magnetic poles are formed in boththe end portions of the wire rope W.

Four peaks 71 a, 71 b, 71 c, 71 d are observed in a range excluding boththe left and right ends 81, 82 of the waveforms shown in FIG. 9 . Thesepeaks 71 a to 71 d appear in the waveforms due to the presence of thedamage in the wire rope W. The higher the degree of the damage is, thelarger these peaks become.

When the occurrence and the degree of the damage are judged by utilizingthe waveforms of the magnetic flux amounts shown in FIG. 9 , forexample, by using threshold values, there is a possibility that thestand-up of both the left and right ends 81, 82 is judged as damagedparts. Thus, in the signal processor 90, correction processing shownbelow is performed.

Returning to FIG. 7 , first, simple moving average processing isperformed (step 63). Regarding a section where a moving average iscalculated, given that sampling is performed for every 1 ms, forexample, the section is about 10 ms. FIG. 10 shows waveforms smoothed byperforming the simple moving average processing on the waveforms of themagnetic flux amounts shown in FIG. 9 .

Next, polynomials of waveforms approximating the moving averagewaveforms are calculated and polynomial fit weighted moving averageprocessing is performed (step 64). This is also processing forsmoothing. For example, by using the least squares method, coefficientsof seventh-order approximation formula are calculated. FIG. 11 showswaveforms smoothed by performing seventh-order polynomial fit weightedmoving average processing on the waveforms after the simple movingaverage processing shown in FIG. 10 .

Finally, the waveforms of the magnetic flux amounts after smoothing(FIG. 11 ) are subtracted from the waveforms of the original magneticflux amounts (FIG. 9 ), and thereby, the waveforms of the magnetic fluxamounts are corrected (step 65). FIG. 12 shows waveforms of magneticflux amounts after correction processing.

It is found that regarding the waveforms of the magnetic flux amountsafter the correction processing, the large stand-up in both the ends isconsiderably smaller than the waveforms of the original magnetic fluxamounts (FIG. 9 ).

If required, the correction processing described above, that is, thesimple moving average processing, the polynomial fit weighted movingaverage processing, and the subtraction processing are repeated (YES instep 66). In subtraction processing for the second time or later, thewaveforms of the magnetic flux amounts after the correction processingcalculated in the previous processing are subtracted. By repeating thecorrection processing, the stand-up of both the end parts can be furthersmaller.

In the waveforms of the magnetic flux amounts after correction, noisesof both the ends (waveform parts of the large stand-up) are removed andthe damaged parts present in the wire rope W correspond to the peakvalues. That is, the S/N ratio of the waveforms of the magnetic fluxamounts (output signals) is improved by the correction processingdescribed above, and it is possible to more accurately detect theoccurrence of the damage to the wire rope W, and the degree and theoccurrence place of the damage. It is possible to acquire signalsconvenient for judging the occurrence of the damage, and the degree andthe occurrence place of the damage by using the threshold values.

What is claimed:
 1. A damage detection method of a wire rope using aportable damage detection device which is provided so as to surround apart of the wire rope in the longitudinal direction over the entirecircumference, the portable damage detection device including amagnetizing device that magnetizes the wire rope in the longitudinaldirection, and a search coil that detects a change in the crosssectional area of the wire rope in an inspection range magnetized by themagnetizing device, the search coil being arranged in an annular shapeto surround a part of the wire rope in the longitudinal direction overthe entire circumference; the damage detection method comprising: movingthe damage detection device back and forth on the wire rope thepredetermined number of times across the inspection range ofpredetermined length of the wire rope thereby aligning the magnetizationdirections in the inspection range of the wire rope; and after themagnetization directions are aligned, recording signals outputted fromthe search coil.
 2. The damage detection method of the wire ropeaccording to claim 1, wherein the damage detection device is moved untilthe damage detection device exceeds both ends of the inspection range ofthe predetermined length of the wire rope.
 3. The damage detectionmethod of the wire rope according to claim 1, wherein the damagedetection device is moved back and forth at least three times.
 4. Aportable damage detection device including a moving mechanism,comprising: a portable damage detection device including a magnetizingdevice which has a columnar internal space through which a wire ropepasses, the internal space having a diameter larger than a diameter ofthe wire rope, the magnetizing device that magnetizes the wire rope inthe longitudinal direction, the magnetizing device being arranged in anannular shape, and a search coil that detects a change in the crosssectional area of the wire rope in an inspection range magnetized by themagnetizing device, the search coil being arranged in an annular shapeto surround a part of the wire rope in the longitudinal direction overthe entire circumference; and a moving mechanism including rotatablesupport rollers respectively attached to both end portions of theportable damage detection device at equal angle intervals, the supportrollers that support the wire rope from four directions around the wirerope at both the end portions, wherein the respective support rollers inboth the end portions of the portable damage detection device areattached in such a manner that the cross sectional center of the wirerope matches with the cross sectional center of the internal space ofthe magnetizing device.